Optimization of Cu/Sn wafer-level bonding based upon intermetallic characterization

The aim of this study is to optimize the bond process for Cu/Sn wafer-level bonding, a competitive material for modern MEMS encapsulation due to its low cost and high performance. For this Solid-Liquid Interdiffusion (SLID) bonding technique, it is important to understand the formation of the intermetallic compounds (IMCs), which takes place during the bond process. In order to estimate thermodynamic kinetics coefficients, electroplated Cu/Sn multilayer stacks were annealed at temperatures in the range 150–300°C for 0–320 min. The formation process of intermetallic compounds (IMC) were investigated by cross-section microscopy of annealed samples at different time and temperature. The kinetics constants of Cu3Sn growth, as well as decreasing Sn thickness, are derived from measured IMC thicknesses. Based upon these extracted kinetics constants, a simulation model for IMC growth and remaining Sn thickness profile during wafer bonding process has been implemented by MATLAB. This model is used to predict an optimized wafer-level Cu/Sn bonding process.